Design and Development of a Switchable Joint for Rehabilitation Purpose with the Focus on an Elbow Joint

Abstract

Artificial elbow modules are used in orthoses and prostheses, whereby orthoses correct, align and support the body with skeletal or neuromuscular impairments [1]. Instead, prostheses replace missing body parts and compensate for lost functions [1]. However, most designs do not allow the natural arm swing based on their transmission design or the devices use multiple actuators to achieve a compliant mode [2]. Consequently, the Scuola Superiore Sant’Anna (Pisa, Italy) developed an elbow module, which can switch between two transmission stages resulting in three selectable elbow modes (locked, free, compliant). Furthermore, it uses only one controlled input leading to a reduced power consumption. Yet, the design contains major problems regarding its selecting mechanism (based on involuntary created moments), weight and dimensions. Here we introduce a new design with the potential to outperform the previous design regarding its unlocking torque, weight and dimensions based on the retrieved results. Hence, the unlocking torque decreased by a factor of 9.2±4.1 to 124.1±35 Nmm and 606.2±97.6 Nmm when 450 g - 600 g were applied. The weight is reduced by ~280 g reaching ~410 g. The diameter and depth are reduced by 7 mm and 5 mm leading to a final size of 78 mm and 32 mm, considering the first stage in combination with a second stage concept. Yet, to prove that the entire introduced design surpasses the previous mechanism, the second stage needs to be finalized, manufactured and tested. However, we provide a successful
design of the first stage that can be used for further investigations.